There is an enormous body of information about the behavior of building walls and numerous guidelines, codes and standards to assist designers in establishing wall performance criteria, selecting and specifying wall materials, and testing to verify wall performance. There is so much information available that it is difficult for a designer to be familiar with and to digest all of it. Guidelines also change over time, often in a way which significantly changes the meaning of performance criteria. In addition, the nomenclature used in this body of information is not clearly and consistently defined. This can make a designer's task difficult, necessitating attention to the current meaning of the guidelines and how changes could impact a design. Examples of ambiguities and contradictions in standards and industry practices are discussed.